The number of documented compounds-including the 9-oxa-3,7-diazabicyclo-[3.3.1]nonane (oxabispidine) structure is very few. As a result, there are very few known processes that are specifically adapted for the preparation of oxabispidine compounds.
Certain oxabispidine compounds are disclosed in Chem. Ber. 96(11), 2827 (1963) as intermediates in the synthesis of 1,3-diaza-6-oxa-adamantanes.
Hemiacetals (and related compounds) having the oxabispidine ring structure are disclosed in J. Org. Chem. 31, 277 (1966), ibid. 61(25), 8897 (1996), ibid. 63(5), 1566 (1998) and ibid. 64(3), 960 (1999) as unexpected products from the oxidation of 1,5-diazacyclooctane-1,3-diols or the reduction of 1,5-diazacyclooctane-1,3-diones.
1,3-Dimethyl-3,7-ditosyl-9-oxa-3,7-diazabicyclo[3.3.1]nonane is disclosed in J. Org. Chem. 32, 2425 (1967) as a product from the attempted acetylation of trans-1,3-dimethyl-1,5-ditosyl-1,5-diazacyclooctane-1,3-diol.
International patent application WO 01/28992 describes the synthesis of a wide range of oxabispidine compounds, which compounds are indicated as being useful in the treatment of cardiac arrhythmiias. Amongst the compounds disclosed are a number that bear a N-2-(tert-butoxycarbonylamino)ethyl substituent.
International patent application WO 02/083690 discloses inter alia a process for the preparation of a compound of formula I,
wherein R1 represents H or an amino protective group and R2 represents C1-6 alkyl (optionally substituted and/or terminated by one or more substituents selected from —OH, halo, cyano, nitro and aryl) or aryl, wherein each aryl and aryloxy group, unless otherwise specified, is optionally substituted;which process comprises reaction of a compound of formula II,
wherein R1 is as defined above, with either:    (i) a compound of formula III,
     wherein R16 represents unsubstituted C1-4 alkyl, C1-4 perfluoroalkyl or phenyl, which latter group is optionally substituted by one or more substituents selected from C1-6 alkyl, halo, nitro and C1-6 alkoxy, and R2 is as defined above; or    (ii) acrylamide, followed by reaction of the resulting intermediate of formula IV,
     wherein R1 is as defined above, with an alcohol of formula R2—OH and an agent that promotes, or agents that in combination promote, rearrangement and oxidation of the compound of formula IV to an intermediate isocyanate, which may then react with the alcohol of formula R2—OH, wherein R2 is as defined above.
The above application also discloses a process for the preparation of a compound of formula I in which R1 represents H, which comprises the preparation of a corresponding compound of formula I in which R1 represents an amino protective group by processes described therein, followed by removal of the amino protective group from that compound. It also discloses in Example 3 Alternative II that [2-(7-benzyl-9-oxa-3,7-diazabicyclo[3.3.1]-non-3-yl)ethyl]carbamic acid tert-butyl ester 2,4,6-trimethylbenzenesulfonic acid salt was converted into the free base with aqueous sodium hydroxide. The [2-(7-benzyl-9-oxa-3,7-diazabicyclo[3.3.1]non-3-yl)-ethyl]carbamic acid tert-butyl ester obtained was hydrogenated in the presence of citric acid and 5% Pd/C to give [2-(9-oxa-3,7-diazabicyclo[3.3.1]non-3-yl)ethyl]carbamic acid tert-butyl ester which was reacted directly without further purification to give (2-(7-[3-(4-cyanoanilino)propyl]-9-oxa-3,7-diazabicyclo[3.3.1]non-3-yl)-ethyl)carbamic acid tert-butyl ester.
Certain novel solid salts of have now been found which offer advantages over known methods.